1. Field of the Invention
This invention relates to a disk driving device for rotating a disk such as a magnetic disk on which data are recorded, and, more particularly, to a configuration of a disk mounting surface thereof on which such a disk is mounted.
2. Description of the Related Art
An example of a conventional disk driving device adapted to rotate a magnetic disk or the like is as shown in FIGS. 9 through 12. The disk driving device, as shown in FIGS. 9 through 12, includes a cylindrical spindle hub 30, on which disks 23A and 23B are mounted.
The spindle hub 30 is integral with the rotor of a disk driving motor. The disk driving motor has a drive magnet 32, which is mounted on the inner surface of the cylindrical wall of the spindle hub 30.
As described above, the spindle hub 30 is cylindrical. More specifically, the configuration of the spindle hub 30 is such that a plurality of cylinders are stacked which are different in diameter. The spindle hub 30 has a disk mounting portion 24 in the form of a flange where the spindle hub is changed in diameter. The disk mounting portion 24, as shown in FIG. 10, has a disk mounting surface 25.
Two disks 23A and 23B are mounted on the disk mounting surface 31 with a spacer 31 therebetween. That is, the disk 23B, the space 31, and the disk 23A are mounted on the disk mounting surface 31 in the stated order. A retaining member 26 is placed on the upper surface of the disk 23A. More specifically, the retaining member 26 has holes which are in alignment with a plurality of threaded holes 28 formed in the spindle hub 30, respectively. A plurality of screws 27 are screwed through the holes of the retaining member 26 into the threaded holes 28 of the spindle hub 30, thus fixedly securing the retaining member 26 to the spindle hub 30. As a result, the two disks 23A and 23B are fixedly secured onto the disk mounting surface 25 of the spindle hub 30. In this operation, it should be noted that the screws 27 are all tightened with a predetermined tightening torque.
In the disk driving device designed as described above, in order to improve the straightness of the disk mounting surface 25 with respect to the axis of rotation of the spindle hub 30, the disk mounting surface 25 is machined. After being machined, the straightness of the disk mounting surface 25 is measured with respect to each point on a linear portion of the disk mounting surface 25 which is extended from the point a to the point b (FIG. 11) (hereinafter referred to as "a linear portion a-b", when applicable). The results of the measurement are as indicated in a graphical representation of FIG. 13. Connecting the peaks of the polygonal lines in the graphical representation forms a line which represents the straightness of the linear portion a-b. It can be determined from the graphical representation of FIG. 13 that the disk mounting surface 25 is substantially perpendicular to the axis of rotation of the spindle hub 30; in other words, the disk mounting surface 25 is substantially horizontal.
In the above-described conventional disk driving device, straightness is employed for indication of the accuracy of the disk mounting surface. However, it goes without saying that other scales may be employed for this purpose; for instance, parallelism may be employed which indicates to what degree the disk mounting surface is parallel with respect to a reference surface which is used for installation of the motor.